Document the BN library.

doc/crypto/BN_num_bytes.pod

@@ -0,0 +1,37 @@
+=pod
+
+=head1 NAME
+
+BN_num_bits, BN_num_bytes, BN_num_bits_word - Get BIGNUM size
+
+=head1 SYNOPSIS
+
+ #include <openssl/bn.h>
+
+ int BN_num_bytes(const BIGNUM *a);
+
+ int BN_num_bits(const BIGNUM *a);
+
+ int BN_num_bits_word(BN_ULONG w);
+
+=head1 DESCRIPTION
+
+These functions return the size of a B<BIGNUM> in bytes or bits,
+and the size of an unsigned integer in bits.
+
+BN_num_bytes() is a macro.
+
+=head1 RETURN VALUES
+
+The size.
+
+=head1 SEE ALSO
+
+bn(3)
+
+=head1 HISTORY
+
+BN_num_bytes(), BN_num_bits() and BN_num_bits_word() are available in
+all versions of SSLeay and OpenSSL.
+
+=cut